The present invention relates in general to power switching modules for half-bridge inverters, and, more specifically, to inverter drive systems for electrified vehicles wherein the power switching modules in the inverter employ enhanced common source inductance to obtain high switching efficiency.
Electric vehicles, such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs), use inverter-driven electric machines to provide traction torque to the wheels. A typical electric drive system may include a DC power source (such as a battery pack or a fuel cell) coupled by contactor switches to a variable voltage converter (VVC) to regulate a main bus voltage across a main DC linking capacitor. An inverter is connected between the main buses and a traction motor in order to convert the DC bus power to an AC voltage that is coupled to the windings of the motor to propel the vehicle.
The inverter includes transistor switching devices (such as insulated gate bipolar transistors, IGBTs) connected in a bridge configuration with a plurality of phase legs. Each phase leg is constructed as a half bridge with a high-side transistor connected in series with a low-side transistor between the DC buses. A typical configuration includes a three-phase motor driven by an inverter with three phase legs. An electronic controller turns the switches on and off in order to invert a DC voltage from the bus to an AC voltage applied to the motor. The inverter may pulse-width modulate the DC link voltage in order to deliver an approximation of a sinusoidal current output to drive the motor at a desired speed and torque. Pulse Width Modulation (PWM) control signals applied to the gates of the IGBTs turn them on and off as necessary so that the resulting current matches a desired current.
Semiconductor switching devices such as an IGBT or a MOSFET are driven at a gate terminal by a gate signal provided by a driver circuit. For an IGBT, the gate signal is applied between the gate terminal and an emitter terminal of the device. In the ON state, an output signal is conducted through the device between a collector terminal and the emitter terminal. Device current flows in a gate loop and in a power loop.
Common source inductance refers to an inductance shared by the main power loop (i.e., the drain-to-source or collector-to-emitter power output of the transistor) and the gate driver loop (i.e., gate-to-source or gate-to-emitter) in a power switching transistor. The common source inductance carries both the device output current (e.g., drain to source current) and the gate charging/discharging current. A current in the output (power loop) portion of the common source inductance modifies the gate voltage in a manner that reinforces (e.g., speeds up) the switching performance. As disclosed in co-pending U.S. application Ser. No. 15/341,184, entitled “Inverter Switching Devices with Common Source Inductance Layout to Avoid Shoot-Through,” filed Nov. 2, 2016, and hereby incorporated by reference, the reduced switching time may be desirable since it may have an associated reduction in the energy consumed (i.e., lost) during the switching transition. The magnitude of the gate loop inductance and/or the power loop inductance and the degree of mutual coupling between them can be manipulated (e.g., enhanced) by selecting an appropriate layout and/or including added overlapping coils in PCB traces forming conductive paths to the transistor gates or emitters in order to obtain a desired common source inductance.
The transistor switching devices and associated components (such as a reverse diode across each transistor) are often packaged in a power module. One typical configuration uses direct bond copper (DBC) substrates having a copper layer with etched circuit patterns which receive transistor and diode dies. After adding bonded jumper wires, terminal pins, and conductive spacers, a module containing two DBC substrates may be encapsulated in an overmolded plastic body.
A power module for use in vehicle electric drive systems must satisfy stringent requirements concerning reliability, efficiency, durability, and cost. Another important consideration is packaging size. When adding structures or components to increase the common source inductance between the gate loop and power loop, the packaging size for a power module has been increased. Thus, it would be desirable to increase common source inductance without significant increase in components or packaging space.